1. Technical Field
The subject of the invention is a DC energy supplying into the 1 phase utility network without transformer. The invention deals with a PV array energy conversion, too.
2. Background Art
It is well known that the H bridges are often applied for direct current energy conversion and feeding into utility network without isolation transformer.
There are various gating patterns for controlling H bridges. However, for the PV application, the useful solutions are limited due to the PV array stray capacitance to the ground. So the usual solution is gating one diagonal with a pulse width modulation (PWM) signal in positive half period whilst the other diagonal is prohibited. The other diagonal is gated with a PWM signal in the negative half period whilst the previous one is prohibited. The two diagonals change role in every half utility network period.
It is also well known that such a gating system can provide only two voltage levels on the output on the H bridge, namely, positive or negative voltage if the AC current is not discontinuous.
The disadvantage of this type of circuit arrangement and control method is that the L,C or L,C,L filter on the output of the H bridge is bigger if it is compared to a multi level system.
It shall be mentioned that further drawback is the unnecessary energy swing between the output filter circuit and the H bridge DC filter capacitor in every PWM period.